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lib/content/elemHideEmulation.js

Index: lib/content/elemHideEmulation.js
===================================================================
--- a/lib/content/elemHideEmulation.js
+++ b/lib/content/elemHideEmulation.js
@@ -755,23 +755,23 @@
       },
       MIN_INVOCATION_INTERVAL - (performance.now() - this._lastInvocation));
     }
     else if (this.document.readyState == "loading")
     {
       this._scheduledProcessing = {stylesheets, mutations};
       let handler = () =>
       {
-        document.removeEventListener("DOMContentLoaded", handler);
+        this.document.removeEventListener("DOMContentLoaded", handler);
         let params = Object.assign({}, this._scheduledProcessing);
         this._filteringInProgress = true;
         this._scheduledProcessing = null;
         this._addSelectors(params.stylesheets, params.mutations, completion);
       };
-      document.addEventListener("DOMContentLoaded", handler);
+      this.document.addEventListener("DOMContentLoaded", handler);
     }
     else
     {
       this._filteringInProgress = true;
       this._addSelectors(stylesheets, mutations, completion);
     }
   },